Cam control means for relief grinding apparatus



May 20, 1969 G. STADE 3,444,653

CAM CONTROL MEANS FOR RELIEF GRINDING APPARATUS Filed May 16', 1967 Fig. 2

Inventor: GER HHRD STHOE MMMMM United States Patent 3,444,653 CAM CONTROL MEANS FOR RELIEF GRINDING APPARATUS Gerhard Stade, Berlin, Germany, assignor to Herbert Lindner G.m.b.H., Berlin, Germany Filed May 16, 1967, Ser. No. 638,836 Claims priority, application Germany, May 18, 1966, L 53,629 Int. Cl. 1324b 5/04, 49/00 U.S. Cl. 51165 8 Claims ABSTRACT OF THE DISCLOSURE The disclosure relates to relief grinding apparatus in which relative movement of a grinding disk and the workpiece toward and away from each other is effected under the control of cam follower means engaged with cam means rotatable with a control shaft. The cam follower means are engaged with the cam means during a working stroke of the grinding disk, and are disengaged from the cam means during a faster return stroke.

The cam control means of the disclosure involves a pair of control cams fixed in axially spaced adjacent relation on the control shaft, these cams being mirror copies of each other and having a relative angular displacement such that the distance, diametrically of the control shaft, between diametrically opposite peripheral points of the two cams, is constant in all angular positions of the control shaft. A pair of levers are provided, each mounted for oscillation in the general plane of a respective cam, and each lever carries a respective cam follower thereon at an end thereof, with each cam follower being engaged with the associated cam and the respective points of cam engagement being at opposite ends of a diameter through the control shaft. The cam followers are moved into and out of engagement with the respective cams by a respective fluid pressure actuator each including a cylinder and a piston, with each piston being connected to a respective lever.

A first unstricted pressure medium circuit is connected in parallel to first corresponding volumes of the two cylinders, and a second unstricted pressure medium is connected in parallel to second corresponding volumes of the two cylinders, the first and second corresponding volumes being at opposite sides of the respective pistons. A reversing valve means is interposed between the source of working fluid under pressure and the two pressure medium circuits, and is selectively operable to supply pressure medium to the cylinders either in a direction to force both cam followers simultaneously into engagement with the cams, during a working stroke of the grinding disk, or to retract both cam followers simultaneously from the cams for a return stroke of the grinding disk.

Background of the invention The invention relates to relief grinding apparatus including a grinding disk engageable with a workpiece, and, more particularly, to a novel and improved cam and cam follower means controlling relative movement of the grinding disk and the workpiece toward each other.

In apparatus of this type, a cam follower, such as a roller, is mounted on a lever and is biased into engagement with the peripheral surface of a cam by suitable means such as, for example, a hydraulic piston connected to the lever. The cam follower or roller is engaged with the cam during a working stroke of the cam, and is retracted from the relief grinding cam during a rapid retraction movement of the grinding disk or wheel.

Such relief grinding apparatus is particularly useful in the grinding of hob-type milling cutters and thread cutters, as well as in the grinding of threaded drills and the like. However, it is also useful in relief grinding workpieces not having a helical tool path such as, for example, roller tools. These workpieces are relief ground in order to obtain the free angle necessary to provide proper cutting capacity of the tool.

The quantity of chips necessary to be removed during relief grinding is relatively small. Thus, the grinding disk remains stable and has sufiicient resistance even if it is subjected to considerable stresses. As a result, workpieces can be worked for relief grinding purposes at high speeds relative to the workpiece and at high rotational speeds of the workpiece or of the grinding wheel or both. The number of relief grinding strokes is thus very large, so that the mass forces occurring at the reversal of movement of the workpiece or of the grinding disk slide constitute a very disturbing factor.

As a general rule, the cam follower roller which transmits the change in radius of the relief grinding cam to the relief grinding means, such as the slide mounting the relief grinding disk or wheel, is pressed by suitable biasing means, such as weights, hydraulic actuators, or springs against a relief grinding cam. The relief grinding movement remains constant and uniform as long as the mass forces occurring during reversal of relative movement of the grinding wheel and work are smaller than the contact force between the cam roller and the cam. This contact force acts on only one side of the relief grinding cam and its bearing. Its magnitude is thus limited, and the number of relief grinding strokes per minute is not allowed to exceed a predetermined value for any particular machine and for any particular length of stroke. If this value is exceeded, the contact or bearing forces are no longer sufficient to maintain the cam roller constantly engaged with the surface of the relief grinding cam. Consequently, the roller will start to jump or vibrate and not only can this jumping or vibration be clearly heard but it also generates, at the workpiece, a relief grinding movement which is undefined or uncontrolled with respect to form and magnitude.

The simplest way of controlling the mass forces is to use a relief grinding cam which has an eccentric shape, and which provides a relief grinding movement of sine shape and of varying speed, with the speed of movement increasing on both sides of the zero or reversal point of the sine curve. This non-uniform speed, however, has considerable disadvantages. In particular, no relief grinding effect can be obtained at the reversal point.

U.S. Patent No. 3,080,684 discloses relief grinding apparatus in which the cam means comprises two archimedial relief grinding cams for positive transmission of the cam control movement. The two cams have identical shapes, are fixed on the control shaft in closely adjacent axially spaced relation, and have a relative angular relation such that, with respect to two cam rollers, they conjointly form a body having dimensions diametrically of the control shaft such that the distance between the axis of the two cam rollers remains constant in all angular positions of the control shaft. The two levers supporting the rollers form a parallelogram-like structure, and this structure, in accordance with the contour of the relief grinding cam means, swings aboutits axes with the movement thereof being positively transmitted to the grinding disk or wheel. Thus, the axis of the grinding disk or wheel performs a movement relative to the workpiece, so that the latter is relief ground without the mass forces, occurring at the reversal points, lifting off or disengaging the cam rollers from the respective relief grinding cams.

In order to uncouple, during one way grinding, the relief grinding movement during the rapid return stroke of the grinding wheel, the arrangement of U.S. Patent No. 3,080,684 provides that the two cam rollers, which are rigidly connected with each other, are lifted from the relief grinding cams. For this purpose, one of the roller supporting levers has a fixed axis of oscillation and the roller supporting lever has an adjustable axis of oscillation.

This positive relief grinding arrangement has certain disadvantages. For example, the positive movement effect is obtained only if the body is exactly of the same thickness throughout. Even at relatively insignificant deviations of the cam shape, a nonuniform movement of the relief grinding cam, with jumping of the cam roller, is possible. Another disadvantageous feature is that the cam rollers are not disengaged simultaneously from the respective cam, but sequentially. It thus can happen, due to the time delay of the disengagement movement, that the relief grinding cam, during the rapid return stroke of the grinding wheel, cannot operatively influence the movement of the latter to be lifted cam roller. Also, the mass forces remain as such and act, in the system which is thus moved in a positive manner, on the transmission elements. The resistance capabilities of the latter relative to the mass forces determine, in the construction of this U.S. patent, the uniform occurrence or movement of the relief grinding and thus of the relief grinding strokes.

Summary of the invention The present invention takes into account the disadvantages of the above-mentioned positive relief grinding'arrangement, and provides a new solution to the problems encountered during relief grinding. The invention starts with the known roller supporting lever which transmits the relief grinding movement in accordance with the change in radius of the relief grinding cam, and which is pressed by a hydraulic actuator toward the relief grinding cam.

In accordance with the invention, the cam roller of one roller lever is positioned diametrically opposite a counter pressure roller mounted on another roller lever, the two rollers being at opposite ends of a diameter through the contol shaft and both engaging a relief grinding cam. The two roller supporting levers are coupled by two pressure medium circuits which are independent of each other, connected in parallel, and unrestricted. These pressure medium circuits are connected, respectively, to the outer and inner corresponding sides of the pistons operating in two working cylinders, and the two pressure medium circuits are connected through a reversing valve to a source of pressure medium. The reversing valve is switchable between forward pressure, idling and reverse pressure.

Due to the unrestricted hydraulic coupling of the takeoff cam roller and its diametrically opposing counter pressure roller, the mass forces are surprisingly controlled in an advantageous manner. This is also the case if, as is advantageous, the take-off roller and the counter pressure roller run on cam shapes providing a constant distance between the axes of the two rollers. In this construction, the exactness of the contours of the cam is not so important, since both rollers are pressed independently of each other against the peripheral surfaces of their associated cams.

In accordance with an advantageous embodiment of the invention, the discharge line of the inner pressure medium circuit includes a throttling means or valve, while a discharge line of the other outer pressure medium circuit is unrestricted. With this arrangement, an increased smoothness of movement of the relief grinding cams with respect to the two roller mounting levers is obtained without effecting the rapid disengagement of the two cam rollers from the respective relief grinding cams during the rapid return movement of the grinding wheel or disk.

The bearing or contact pressure of the cam rollers against the cams should preferably be adjustable to obtain a better control of the mass forces. For this reason, it is further not necessary that the masses which are moved during the relief grinding be maintained as small as possible, as contrasted to the prior art constructions wherein these masses have been kept as small as possible. In order to make the relief grinding cam movement as uniform as possible, larger masses may be advantageous.

An advantageous embodiment of the invention involves movement of the roller supporting lever carrying the takeoff cam roller being transmitted through an intermediate lever as a translatory movement of the grinding slide which is accomplished by a push rod connected to the slide and to the intermediate lever. This arrangement is particularly advantageous for larger relief grinding strokes.

Accordingly, an object of the present invention is to provide an improved cam control arrangement for relief grinders.

Another object of the invention is to provide such an improved cam control arrangement for relief grinders involving positive displacement of the grinding means responsive to the angular position of control cam means.

A further object of the invention is to provide such a cam control including a take-off cam roller and a counter pressure roller, the two rollers being at opposite ends of a diameter through a control shaft mounting control cams, one engaged by each roller and with the control cams being so related that the distance between the axes of the two rollers remains constant in all angular positions of the control shaft.

Still another object of the invention is to provide such an arrangement in which each of the two rollers is mounted at the end of a respective lever and the two levers are connected to the pistons of fluid pressure actuators each including a cylinder, with corresponding volumes of the two cylinders being supplied in parallel from respective fluid pressure medium circuits.

A further object of the invention is to provide an arrangement of the type just described, in which the two pressure medium circuits are connected through a reversing valve to a source of fluid under pressure, the reversing valve being selectively operable to apply fluid under pressure to the outer surfaces of the two pistons, to the inner surfaces of the two pistons, or to idle the fluid pfessure actuators.

Yet another object of the invention is to provide an arrangement of the type just mentioned in which the return or discharge circuit of the pressure medium circuit connected in parallel to the inner volumes of the two cylinders includes a throttling or valve means, whereas the pressure medium circuit connected to the outer volumes of the two cylinders has a substantially unrestricted return or discharge circuit.

A further object of the invention is to provide a cam control arrangement for relief grinders in which the relief grinding means is positively displaced in accordance with the contour of a relief grinding cam, and which ensures a smooth movement of the cam and cam engaging rollers, without any possibility of the rollers disengaging the cam surfaces inadvertenly during a working stroke of the grinding means, with both rollers being positively disengaged simultaneously from the relief grinding cam means during a rapid return stroke of the grinding means.

Brief description, of the drawings For an understanding of the principles of the invention, reference is made to the following description of atypical embodiment thereof as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a somewhat diagrammatic vertical sectional view of a relief grinding arrangement embodying the invention, with the parts as they appear during a working stroke; and

FIG. 2. is a view of a portion of FIG. 1 illustrating the parts as they appear during the rapid return movement of the relief grinding means.

Description of the preferred embodiments Referring to the drawing, a machine frame 1 carreis a workpiece slide 2 and a grinding wheel slide 3. Slide 2 has longitudinal guides 4 and -5 for a translatory reciprocation of workpiece 6 relative to grinding disk or wheel 7. The relief grinding movement is effected perpendicular to the workpiece and in the direction of the double arrow 8 of FIG. 1. For this purpose, grinding slide 3 has a transversely extending guide 9 which extends perpendicular to the longitudinal guides 4 and 5. The mounting of the grinding disk 7 and its drive have not been illustrated, as such arrangements are well known to those skilled in the art.

Grinding wheel slide 3 has a projection 11 extending through an opening in the machine frame or bed 1. A push rod 12 is secured to this projection, adjacent one end of the push rod, and has its other end connected to the relief grinding cam control arrangement which will be described hereinafter. The other end of push rod 12 is pivotally connected to an intermediate lever 12' which is oscillatata-bly mounted, and has its free end connected by a link 12" to an intermediate point on a lever 17.

The relief grinding cam 13 fulfills the requirement of a cam member which has a constant distance between peripheral surface points at opposite ends of a diameter through the axis of the cam, and comprises two cam shapes having archimedrial peripheries. These cam shapes are fixed on a control shaft 14 which is driven from the drive of workpiece 6. The transmission or gearing providing this drive is not shown in detail, but is indicated by the broken line 15. The speed ratio of the relief grinding cam relative to the workpiece is variable, and is dependent on the number of grinding strokes which, in turn, is determined by the number of teeth or the like of the workpiece.

The two cam shapes of cam 13 are indicated at 13' and 13 Take-off cam roller 16 bears against cam shape 13', and roller 16 is mounted at the free end of a roller supporting lever 17 which is oscillatable about an axis 18. Counter pressure roller 19 bears against the second relief grinding shape 13 and is mounted at the free end of a second roller supporting lever 20 which is oscillatable about an axis 21. Each roller is mounted on a respective pin or axle 22 or 23 in the assoicated roller supporting lever, and these pins are connected with respective piston rods 24 and 25. Piston rods 24 and 25 are connected to respective pistons 26 and 27 moving in associated working cylinders 28 and 29.

Working cylinders 28 and 29, which are arranged in substantially axially aligned diametrically opposed relation, are positioned in machine frame 1 below guides 4 and 5 for workpiece slide 2. Corresponding inner volumes of cylinders 28 and 29 are interconnected by an inner pressure medium circuit 30, and corresponding outer volumes of cylinders 28 and 29 are interconnected by an outer pressure medium circuit 31. By the inner volumes are meant those volumes of each cylinder which are defined, in part, by the piston rods 24, 25 and the pistons 26 and 27, and by the outer volumes of the cylinders is meant those volumes which are defined, in part, by the opposite surfaces of the pistons 26 and 27. The pressure medium circuits 30 and 31 are independent of each other and are designed as unrestricted flow pressure medium circuits. The pressure medium circuits are connected to respective supply lines 32 and 33, which also act as return lines. Lines 32 and 33 connect the pressure medium circuits to a reversing valve 34 which is constructed as a magnetic valve and, as shown in the drawings, includes an operating electromagnet 35 operating against the bias of spring 36.

A pressure medium supply line 37 connects valve 34 to a pressure medium pump 38 drawing fluid pressure medium, such as oil or other hydraulic fluid, from a supply 39 and delivering the working fluid, under pressure, to the valve 34 for delivery to working cylinders 28 and 29 in accordance with the relative position of valve 34. Valve 34 has two discharge lines 40 and 41 which return fluid pressure medium to reservoir or container 39. Discharge line 40 contains a throttle means or valve 42, while discharge line 41 has an unrestricted flow cross section. Supply line 37 is provided with an adjustable excess pressure valve 43 or, alternatively, pump 38 may be in the form of a pressure regulating pump.

In the position of reversing valve 34 shown in FIG. 1, supply line 37 is connected to line 33 and thus to the outer pressure medium circuit 31 connected to the outer corresponding volumes of the cylinders 28 and 29, in parallel. The inner pressure medium circuit 30, connected in parallel to the inner pressure volumes of cylinders 28 and 29, is connected to discharge line 40 containing the throttling means or valve 42. This throttling means or valve 42 maintains a lower counter pressure, so that the rollers 16 and 19 do not suddenly engage the peripheral surface of relief grinding cam shapes 13' and 13 The hydraulic bearing or contact pressure causes the pistons 26 and 27 to move toward the relief grinding cam, so that both rollers 16 and 19 are caused to bear against this cam. The magnitude of the bearing pressure is adjustable. For this purpose, the excess pressure valve 43, connected in pressure medium line 37, is provided. The bearing pressure of rollers 16 and 19 against cam 13 results in the cam 13 controlling the relief grinding strokes of grinding means supporting slide 3.

During the rapid return stroke of the grinding means, reversing valve 34 is switched to the position of FIG. 2. In this position, pressure medium line 37 is connected with line 32 and thus to the inner pressure medium circuit 30 which is connected in parallel to the inner volumes of the cylinders 28 and 29. Outer pressure medium circuit 31, and its line 33, are connected through valve 34 to discharge line 41 for unrestricted discharge. Both rollers 16 and 19 are lifted or disengaged simultaneously from the respective cam shapes comprising the relief grinding cam 30. The degree of retraction is limited by the pistons, or abutments on the pistons, engaging the outer end surfaces of the respective cylinders. Grinding disk 7, when disengaged from workpiece 6, is always situated at the same location and can be fed from this location. After the rapid return movement has occurred, reversing valve 34 is again switched into the position of FIG. 1 and the procedure is repeated.

While a specific embodiment of the invention has been shown and described in detail to illustrate the principles of the invention, it will be understood that the inevntion may be embodied otherwise without departing from such principles.

What is claimed is:

1. In relief grinding apparatus of the type including a grinding disk rotatable about an axis which is in spaced parallel relation to a workpiece, the grinding disk and the workpiece being relatively reciprocable parallel to such axis, during alternating working and return strokes, and relatively movable laterally of the direction of reciprocation under the control of cam follower means engaged with cam means rotatable with a control shaft, the improvement comprising, in combination, a relief grinding control cam means fixed on said control shaft; a pair of levers each mounted for oscillation in the general plane of said cam means; a pair of cam followers each mounted at a corresponding end of a respective lever and each engaged with said cam means, the respective points of cam means engagement being at opposite ends of a diameter through said control shaft; said levers and said carn followers constituting said cam follower means; a pair of fluid pressure actuators each including a cylinder and a piston, each piston being connected to a respective lever; fluid circuit means interconnecting corresponding volumes of said cylinders to each other, whereby the pressures and corresponding volumes of said cylinders are equalized; a first unrestricted pressure medium circuit connected in parallel to first corresponding volumes of said two cylinders; a second unrestricted pressure medium circuit connected in parallel to second corresponding volumes of said two cylinders; said first corresponding volumes being at one side of the respective pistons, and said second corresponding volumes being at the opposite side of the respective pistons; a source of working fiuid under pressure; and reversing valve means connected to said source and to said circuits and selectively operable to supply pressure medium to said cylinder either in a direction to force both cam followers simultaneously into engagement with said cam means, or to retract both came followers simultaneously from said cam means.

2. In relief grinding apparatus, the improvement claimed in claim 1, wherein each of said cam followers comprises a cam roller rotatably mounted on a respective one of said levers.

3. In relief grinding apparatus, the improvement claimed in claim 1, in which said relief grinding cam means comprises a pair of cams fixed in axially spaced adjacent relation on said control shaft, said cams being mirror copies of each other and having a relative angular displacement such that the distance, diametrically of the control shaft, between diametrically oposite peripheral points of the two cams is constant in all angular positions of the control shaft.

4. In relief grinding apparatus, the improvement claimed in claim 1, including respective discharge lines selectively connectable to each pressure medium circuit by said reversing valve means; the discharge line for the pressure medium circuit connected to the inner volumes of said cylinders including throttling means, and the discharge line connected to the pressure medium circuit connected to the outer volumes of said cylinders being substantially unrestricted in flow area.

5. In relief grinding apparatus, the improvement claimed in claim 4, in which said throttling means comprises a valve.

6. In relief grinding apparatus, the improvement claimed in claim 1, including means operable to adjust the bearing pressure of said cam followers against said cam means.

7. In relief grinding apparatus, the improvement claimed in claim 1, in which said cam followers are rollers, one roller comprising a take-off roller and the other roller comprising a counter pressure roller; said grinding disk being supported on a slide; an oscillatably mounted intermediate lever connected to the lever supporting said take-01f roller; and a push rod interconnecting said slide and said intermediate lever.

8. In relief grinding apparatus, the improvement claimed in claim 1, in which said fluid presure actuators are hydraulic presure actuators.

References Cited UNITED STATES PATENTS 3,080,684 3/1963 Stade et a1. 5l45 3,267,616 8/1966 Stade et a1 5195 LESTER M. SWINGLE, Primary Examiner.

US. Cl. X.R. 

